Polycarbonate is a thermoplastic that has excellent mechanical properties such as impact resistance, heat resistance and transparency. Polycarbonates are widely used in applications ranging from football helmets to automobile parts to transparent security windows. More recently, polycarbonates have also proven to be the material of choice for optical media applications such as optical discs, for example compact discs (CD) and digital versatile discs (DVD). Conventional polycarbonates are usually produced by (1) an interfacial polymerization, in which bisphenol A (BPA) is reacted directly with phosgene or by (2) a melt polymerization process in which BPA is transesterified with a diaryl carbonate such as diphenylcarbonate (DPC) or an activated diaryl carbonate such as bismethylsalicylcarbonate (BMSC). For many applications, there has been a need for materials possessing the fundamental characteristics of transparency and toughness inherent in BPA polycarbonate but possessing, in addition, certain improvements in physical properties relative those possessed by bisphenol A polycarbonate (BPA-PC), for example birefringence. For some applications improved chemical resistance relative to BPA polycarbonate is required, for example in certain medical and automotive applications. Copolycarbonates are materials frequently possessing the fundamental traits of BPA polycarbonate, transparency and toughness, but in certain instances also possessing improved performance characteristics for a given application relative to BPA polycarbonate.